48 EXCURSIONS IN MADEIRA 



I had taken the angle of elevation of the Peak of Kuivo with a 

 reflecting circle, from the'point generally visited by strangers for 

 the best view of the Coural, and adjoining the Pico das Bordas, 

 knowing that I could get its horizontal distance from Euivo very 

 accm-ately from Lieutenant Colonel Paulo Dias d 'Almeida's survey, 

 just completed, after six years' labour, drawn originally on a scale of 

 twenty-eight inches to a Portuguese league, and containing every 

 quinta on the island. My own attempts to get a sufficient base by 

 angles from a smaller one, measured with the aid of an artificial 

 horizon of crystal, and a proof telescope, (lunette d'epreiwej failed 

 from unfavourable weather. 



6 6 20 Apparent angle of Ruivo. 

 26 Refraction". 



6 5 54 Which, with 24,805 feet for the horizontal distance, gives 2578 

 Height of apparent, above true level, for 24,805 feet ... 15 

 Height of point of view above the level of the sea . . . 3710 



Height of Ruivo 6303 

 being 139 feet more™ than that given by the barometer, which was 

 For tin's, and had been compared with that of the observatory for 

 several weeks. M. Von Euch, and Professor Smith, found the 

 Torrinhas (notoriously lower than the Pico Kuivo) 5857 feet 

 above the sea". These circumstances considered, I cannot help 



" To eatimate the terrestrial refraction, (not having Lindenau's tables of negative 

 soefficients,) I followed the method recommended, I think by Pictet, at the end of 

 -le first volume of De Saussure's Travels ; calculating (by Dr. Young's tables) the 

 astronomical refraction at each station, for the angle of elevation under which Ruivo 

 is seen from the lower, (knowing the height of the barometer for each,) and takino- 

 the half on the supposition, which may be made without any sensible error, that the 

 curve between the two stations is circular. This gave me within a fraction of what 

 Dr. Maskelyne allows, viz., ^^ of the intermediate arc : but, if the consideration of 

 the refraction were neglected altogether, it would not make a difference of six feet. 



" M. Pictet's measurement of Mont Blanc, from the glacier of Buet, in a similar 

 manner, exceeded De Luc's direct barometrical measurement by 210 feet. 



^ Narrative of an Expedition to explore the River Zaire. Introduction, p. Ixviii. 

 Ruivo was not accessible at the time of their visit to Madeira. 



